The analysis of particular lethal mutation has demonstrated the existence of neoplasms in Drosophila. The availability of temperature sensitive mutations provides a system in which the initiation of neoplasmic development can be controlled and the consequences analysed. We have isolated and begun the analysis of temperature sensitive alleles at two neoplastic loci, Tum1 and 1(2)gl. The Tum1 mutation develops a neoplasm of the larval lymph gland (1,2), and the 1(2)glts mutation develops a neoplasm of the imaginal wing disc (3,4). The proposed research on the 1(2)glts mutation involves defining: 1) the effect of the induction of tissue regulation on the initiation of neoplastic development, 2) the role of cell death on the initiation of neoplastic development, 3) the consequences of neoplastic development on the tissues ability to perform normal functions, i.e. tissue regulation and hormone response, 4) the change in the rate of clone expansion during neoplastic tissue to recruit developmentally normal tissue into the growing neoplasm and, 6) the role of gamma irradiation in the initiation of neoplastic development. The proposed research on the Tum1 mutation involves defining: 1) the role of the production of differentiated cells in the initiation of neoplastic development, 2) the ability of the lymph gland derived neoplasms to respond to hormone stimulation and, 3) progressive changes that occur during the growth of the neoplasm.